One-Dimensional Compression Behavior of River Silty Sand: Emphasizing the Equivalent Void Ratio Concept

Previously, studies have recognized that the characterization of the compression behavior of sand–silt mixtures that use different void ratio concepts is controversial and incomplete, because most of the earlier studies considered the global or intergranular void ratio as reliable parameters to explain the differences between the mechanical responses of sand–silt mixtures. However, the equivalent void ratio concept could be used as a well-founded alternative to express the compression behavior in mixed soils. To achieve this goal, compression behavior tests on Chlef silty sand were carried out. The specimens were subjected to one-dimensional (1D) oedometer loading conditions that emphasized the application of the global, intergranular and equivalent void ratios concepts. The Chlef sand specimens that were mixed with 0% to 40% silt contents were prepared using two fabric techniques [dry funnel pluviation (DFP) and moist tamping (MT)] at three initial relative densities (D_r = 18%, 52%, and 88%). A detailed analysis was carried out to compare the normal compression characteristics with those that were derived from the intrinsic compression (the normalized compression curves). Based on experimental evidence, this paper introduces a new dependable parameter, the equivalent compression index $(C_c^{\ast })$, which could be obtained from the [ $e^{\ast }\text{–}(\log {\sigma }_v^{\mathrm{\prime }})$] curve. The test results reveal that the equivalent void ratio concept plays a reliable role in the prediction of the compression behavior of the Chlef sand–silt mixtures, where the compressibility parameters of the tested specimens are well normalized using the equivalent compressibility curves for different fines contents that consider both fabric techniques and all selected initial relative densities. Based on the test results, the intrinsic compression characteristics $(C_c^{\mathrm{int}},C_{c-g}^{\mathrm{int}},\mathrm{and}{C}_c^{\ast \mathrm{int}})$ exhibit very similar tendencies compared to those of the normal compression $(C_c,C_{c-g},\mathrm{and}{C}_c^{\ast })$ and a correlation has been suggested between the two different compression characteristics. In addition, a new relationship has been developed that expresses the undrained mechanical characteristics (taken from a previous study) as a function of the obtained compression indexes that consider the effects of all selected parameters under the same experimental conditions.